The present invention relates to a device which makes it possible to determine the forces present between the tire and the travel surface on which it is rolling and furthermore, in particular, permits measurement of the properties of the tire, utilizing the longitudinal forces. Such properties are, for instance, the rolling resistance and the coefficient of longitudinal adherence. The invention also concerns the methods carried out by means of such a device and, more particularly, the methods for the comparative measurement of the properties of rolling resistance and adherence limits of different tires, or the same properties due to different travel surfaces.
Taking into account all the factors which can play a part during the measurement of rolling resistance, this measurement is very difficult and, as known, there are two major kinds of methods: The first kind concerns measurements on machines, and mention may be made of measurements on a flywheel, the tire to be tested traveling on a flywheel of larger or smaller diameter, and measurements on roller test benches, said rollers having small diameters and producing stresses in the tire far different from those encountered on a flat travel surface, hence the appearance of the machine on a flat travel surface in the form of a belt on which the tire rolls; the second type concerns measurements on actual runways and travel surfaces which are generally carried out with a vehicle, whether an analytical vehicle or a conventional vehicle. With this last type of vehicle, the so-called travel-surface-deceleration method is frequently used, which method is undoubtedly less precise than the others, but gives interesting results, since it includes the environmental factors to the maximum extent.
As to the adherence limit measurements, they are also generally carried out with the use of flywheels in the case of measurements on machines, but they are more frequently performed with the use of vehicles traveling on runways with different variable, travel surfaces. It is obvious that the methods with vehicles and runways require considerable space, in the same way as the methods with flywheels, since the flywheels must be of large diameter.